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Toggle navigation Menu. Name of resource. Problem URL. Describe the connection issue. SearchWorks Catalog Stanford Libraries. Handbook of nanophysics [electronic resource]. Responsibility edited by Klaus D. Physical description 7 v. Online Available online. Lower Hutt, New Zealand Hendy Industrial Research Ltd. Wesselinowa, Thomas Michael, and Steffen Trimper Thareja and Antaryami Mohanta There is no comprehensive work related to amorphous nanoparticles and this motivates us to write this chapter on the Handbook of Nanophysics. It is well known that crystalline nanoparticles have a well-defined crystal structure with a large fraction of their atoms located on the surface, including a structural disorder in the vicinity of the sur- face when compared to that of a perfect crystal, which provide them with unique properties that are different from their crys- talline bulk counterparts Changsheng et al.
In contrast, amorphous nanoparticles have a disordered structure, which may be divided into two parts, i. Due to their disordered structure, amorphous nanoparticlescanhavemoreadvancedapplicationsthanacrystal structure with well-defined properties. Due to surface effects, the structure and the proper- ties of amorphous nanoparticles are also different from those of their corresponding amorphous bulk-counterparts.
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Therefore, amorphous nanoparticles have attracted a great interest and have been under intensive investigation in the recent years Libor et al. Much attention has been paid to the synthesis and the characterization of amorphous nanoparticles; therefore, important methods for the synthesis of amorphous nanoparticles have been listed in a subsequent section of the chapter.
On the other hand, in order to get structural informa- tion about amorphous nanoparticles, one can use several dif- fraction techniques. However, more detailed information of the microstructure of amorphous nanoparticles at the atomic level can be provided by a computer simulation.
Therefore, we also discuss the results obtained by a computer simulation of amor- phous nanoparticles. Moreover, the physicochemical properties of amorphous nanoparticles have been under intensive investi- gation by both experiments and computer simulations Hoang a, Libor et al. In particular, amorphous nano- particles can have advanced catalytic properties compared with traditional crystalline catalysts or good magnetic materials, etc. Therefore, applications of amorphous nanoparticles have also been given considerable attention in the chapter.
Our aim here is not to review the methods 1 Amorphous Nanoparticles 1. Note that, we focus attention only on the methods of the synthesis of nanopowders of amor- phous nanoparticles without the presence of matrices or other supported materials. It was found that the size, the shape, and the size distribution of amorphous nanopowders depend on the method of synthesis used in practice Libor et al.
It seems that chemical reduction has often been used for the synthesis of amorphous nanoparticles of alloys rather than for other sub- stances Table 1. Moreover, syntheses based on ultrasound or microwave irradiation have also often been used for the prepara- tion of amorphous nanoparticles in addition to the precipitation methods, and much attention has been paid to sonochemical synthesis in the recent years.
However, two methods which have been widely used in order to characterize the amorphous nature of nanoparticulate samples are XRD and selected area electron diffraction SAED as part of TEM analysis. The absence of Bragg peaks in the XRD pattern is an identification of the amorphous nature of a nanoparticulate sample, which is different from that of nanocrystalline polymorphs, i.
However, the application of XRD for the detection of the amor- phous phase is limited if the samples contain the crystalline matrix or ultrasmall nanocrystalline polymorphs. Further evi- dence of the existence of the amorphous phase is provided by the SAED pattern. The broad, diffusive ring suggests a typical amorphous structure of nanoparticulate samples Figure 1.
Note that the indication of an amorphicity given by the SAED pattern is usually related to a very small number of particles involved in such an analysis and it is its limitation. Therefore, in order to detect the amorphous nature of nanoparticulate samples, additional indirect approaches emerging from the monitoring of thermal and magnetic behaviors, for example, are applicable.
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However, the obtained data are strongly affected by the sample character and the measurement conditions Libor et al. In particular, the SEM of Fe82P11B7 amorphous nanoparticles produced by chemical reduction shows that the sample consists of nearly spherical par- ticles with a diameter ranging from to nm Jianyi et al. From Prozorov, R. B, 59, , With permission. TABLE 1. Amorphous Nanoparticles Similarly, the TEM of amorphous B nanoparticles synthe- sized by the arc decomposing diborane shows that nanopowder consists of nearly spherical particles with an average diameter of 75nm and a narrow size distribution Figure 1.
The narrow size distribution and the ideal spherical shape should be attrib- uted to the high temperature of the arc Si et al. While the structure of crystalline nanoparticles is well defined, our knowledge of the structure of amorphous nanoparticles is still limited.
Handbook of nanophysics. edited by Klaus D. Sattler - Details - Trove
However, it is evident that they have a short-range structure like that observed for the corresponding amorphous bulk counterparts. In particular, valuable information about the short-range structure and the magnetic behavior of amorphous magnetic nanoparticles such as Fe2O3, Fe3O4, etc.
Further, the ratio of the spectral lines corresponding to the surface and the bulk Fe atoms should strongly relate to the particle size. However, the published data are not consistent with this relation Libor et al. In addi- tion, TEM, XRD, x-ray absorption spectroscopy, and infrared spectroscopy have been used for the structural characterization of partially amorphous SnO2 nanoparticles, i.
In a structural analysis of disordered materials including liquid and amorphous nanoparticles, the radial distribu- tion function RDF , g r , is no doubt of the chosen value. It yields the central information about the short-range order and serves as a key test for different structures. For simplic- ity, we discuss about g r for monatomic fluids. A schematic explanation of g r of a monatomic fluid can be seen in Figure 1.
The radial distribution function, g r , can be interpreted as the not normalized conditional probability to find another particle a distance r away from the origin, given that there is a particle at the origin. Now, we discuss the physical interpreta- tion of the information that can be gotten from g r. At a small- enough distance, r, the function g r is essentially zero since atoms cannot strongly overlap their electronic shells. Based on Figure 1.
From Zhong, G. Alloy Compd. From Si, P. Note that one can directly calculate g r via the coordinates of all atoms in the models obtained by a computer simulation, i. The function has been averaged over all atoms in the system. In order to get detailed information about the microstructure of amorphous nanoparticles, a combination of experiment and computer simulation is needed. The atomic structure of 2nm amorphous TiO2 nanoparticles has been studied in detail via analysis of PRDFs, bond-length distribution, coor- dination number, and bond-angle distributions. In addition, the structural characteristics of the core and the surface shell of nano- particles have been also analyzed.
It was found that 2nm amor- phous TiO2 nanoparticles consist of a highly distorted surface shell and a small strained anatase-like crystalline core. The reduc- tion in the coordination number of Ti atoms in amorphous TiO2 nanoparticles compared with that observed in the corresponding amorphous bulk indicates the surface effects in the former. On the other hand, the shortening of the Ti—O bond in amorphous TiO2 nanoparticles was suggested to be related to the distorted surface shell in the nanoparticulate samples.
Unfortunately, no more sim- ilar work related to the atomic structure of amorphous nanopar- ticles has been found in literature yet, and our understanding of their microstructure is still limited. Thanks to the results obtained by the computer simulations, our understanding of the atomic structure of liquid and amorphous nanoparticles has been substantially improved. The detailed size and tem- perature dependence of the atomic structure and the various thermodynamic properties of amorphous nanoparticles of dif- ferent substances have been studied.
In particular, the struc- tural properties of amorphous nanoparticles have often been studied in spherical models of different sizes ranging from 2 to 5nm. Models have been obtained by cooling from the melt via classical MD simulation with the pair interatomic potentials. It was found that the peaks in PRDFs of amorphous nanoparticles are broader than those for the bulk, indicating that the structure of nanopar- ticles is more heterogeneous than that for the bulk due to the contribution of the surface structure of the former see, for example, Figure 1.
Moreover, the structural characteristics of amorphous nanoparticles are size dependent, and the mean coordination number increases toward the value of the bulk if the particle size increases due to the reduction of the surface- to-volume ratio Figure 1.
Note that for spherical models of nanoparticles, the non-periodic boundary conditions were g r 1 0 r First coordination shell Second coordination shell Continuum FIGURE 1. The atom at the origin is highlighted by a black sphere. The dashed regions between the concentric circles indicate which atoms contribute to the first and second coordination number shells, respectively. From Ziman, J. Amorphous Nanoparticles used. In contrast, models obtained in a cube under periodic boundary condition were considered as the corresponding bulk counterparts.
Moreover, calculations also show that amorphous nano- particles consist of two distinct parts: the core and the surface shell. The structure of the former is relatively size-independent and close to that of the corresponding bulk while the structure of the latter is strongly size dependent and more porous com- pared with that of the bulk or of the core of nanoparticles.